This invention relates generally to multi-axle transport vehicles for moving heavy loads, and more particularly to a method and apparatus for steering the transport vehicle.
Heavy hauling vehicles for moving transformers, cranes, boats, industrial equipment, and other heavy objects are well known in the art. An example of such a vehicle is shown in U.S. Pat. No. 4,943,078 which discloses a heavy load hauler for traveling on conventional roadways for moving heavy construction equipment such as cranes or the like from one work site to another. The hauler includes a front tractor drawn carriage, a rear carriage, and a load unit between and carried by the carriages. The front carriage is supported upon a multiplicity of independent wheel and axle units. There is a first fifth wheel coupling at the leading end of the front carriage for connecting to the fifth wheel coupling of a tractor. A second fifth wheel coupling is spaced rearwardly. The load carrying rear carriage is also supported upon a multiplicity of independent wheel and axle units. There is a fifth wheel coupling intermediate the leading and trailing ends of the carriage. The load unit has forwardly and rearwardly projecting goosenecks. Each gooseneck has a fifth wheel coupling. The one on the forwardly projecting gooseneck connects to the fifth wheel coupling on the front carriage. The one on the rearwardly projecting gooseneck connects to the fifth wheel coupling on the rear carriage. The load unit may be either the crane itself or a flatbed upon which the crane is carried. At least some of the independent wheel and axle units are steerably mounted on their carriages. Each wheel and axle unit has its wheels supported by a hydraulic suspension. Hydraulic circuitry interconnects all of the suspensions so as to equally distribute the load among all of the wheel units. Steering of the independent wheel and axle units is interphased for the front and rear carriages by a pair of operatively associated interrelated inline valve cylinder units. FIG. 12A shows a valve 718 used in a power steering system which is coupled to a connecting link 703.
Other heavy hauling vehicles are sold by Goldhofer Fahrzeugwerk G.m.b.H. of Memmingen, Germany; Nicolas of Champs Sur Yonne, France; and, Talbert of Renssclaer, Ind.
Improved systems having automatic steering at all speeds and suspension systems that respond rapidly to the varying road conditions imposed by higher speeds would greatly reduce the time and effort required to move the vehicle to the load, move the load, and return the vehicle to storage.
The present invention is directed to a method and device for steering a heavy load transport vehicle. The invention combines a conventional hydraulic power steering valve with a variable length strut to effect steering control. The power steering valve is placed in xe2x80x9cparallelxe2x80x9d across the variable length strut so that as the variable length strut expands and contracts a small distance due to the movement of a tow bar, the power steer valve changes switching states, and though mechanical linkages, causes the transport vehicle to turn in the desired direction. In essence the variable length strut serves as a direction sensor which communicates the desired direction of turn to the power steering valve.
The present invention has a distinct advantage over prior art systems in the event of power steering system failure. The variable length strut will turn the steering system without hydraulic power. When this happens, the variable length strut absorbs the mechanical stresses of turning, thereby protecting the power steering valve. This is in contrast to prior art systems where the power steering valve is installed in series with the strut and is thereby exposed to large mechanical stresses if the power steering system fails.
Additionally, because of the small displacement of the variable length strut, the present invention provides rapid and continuous steering corrections as the transport vehicle is towed down a highway.
In accordance with a preferred embodiment of the invention, a device for steering a transport vehicle having a rotatable tow bar and a front dolly having front wheels is provided and includes:
a variable length strut connected between the tow bar and the front dolly, the variable length strut having a first section and a second section, the first and second sections longitudinally movable with respect to one another;
a hydraulic power steering valve having a first end and a second end;
the first end of the power steering valve connected to the first section of the variable length strut, and the second end of the power steering valve connected to the second section of the variable length strut; and,
wherein when the tow bar is rotated, the first and second sections of the variable length strut longitudinally move with respect to one another causing the power steering valve to assume a hydraulic switching state, the switching state including one of (a) a left state which causes the front wheels of the front dolly to turn in a left direction, and (b) a right state which causes the front wheels of the front dolly to turn in a right direction.
In accordance with an aspect of the invention, when the rotation of the tow bar is stopped, the power steering valve assumes a neutral hydraulic switching state wherein further turning in a left direction or right direction ceases.
In accordance with an aspect of the invention, the first and second sections are longitudinally movable a distance of about 0.13 inches with respect to each other.
Other aspects of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.